Plastics such as acrylonitrile-butadiene-styrene (ABS) and polyphenylene oxide (PPO) are frequently used for plastic parts in the automobile industry. In automotive applications one may want the part to be decorative chromium plated. Decorative chromium plates customarily comprise successive electrodeposited layers of copper, nickel and chromium. One does not want the layers to lose adhesion to the plastic during such electroplating or in corrosive and thermal cycling environments, such as are encountered in outdoor service and environmental testing. In order to get these layers to be durable and adhere well to plastic surfaces, the plastic surfaces have to be prepared in a very special way. This is particularly true of ABS and PPO plastic surfaces.
A typical ABS or PPO plastic surface pretreatment involves etching the plastic surface in a substance such as chromic acid. The plastic surface is then neutralized, and rinsed to remove any residual chromic acid. It is then immersed in a palladium colloid, which serves as a catalyst to trigger a subsequent electroless deposition of a thin blanket of copper or nickel onto the plastic surface. The palladium activation step is quite costly. However, it is important, in that it forms activated adhesion sites on the plastic surface. The plastic surface is then immersed in an electroless plating solution, which deposits an adherent thin metal blanket onto the plating surface. This thin layer of copper or nickel provides an adherent electrically conductive and thus readily platable coating on which to electrodeposit the decorative chrome plate.
One can appreciate that such a succession of steps is time consuming and therefore costly. It should also be appreciated that the palladium colloid is itself an expensive item in the process. Also, the safety precautions and waste disposal steps required when one works with chromic acid are quite expensive. In contrast, we have found that comparable adhesion can be obtained on ABS and PPO by a faster and less costly process. Wet chemistry process steps are avoided completely, as are the problems and costs associated with them.